The technical portion of the work performed by an optician consists in mounting a pair of ophthalmic lenses in a frame selected by a wearer. Such mounting is made up of five main operations:                reading the outlines of the bezels of the rims of the frame selected by the wearer, i.e. the outline of the groove going around the inside of each of the rims of the frame;        centering each lens, which consists in determining the position that each lens is to occupy in the frame so as to be appropriately centered relative to the wearer's eye;        feeling each lens, which consists in determining the coordinates of points characterizing the shape desired for the outline of the lens; then        shaping each lens, which consists in machining or cutting its outline to the desired shape, given the defined centering parameters; and finally        beveling, which consists in forming a bevel that is to hold the lens in the bezel included in the frame.        
In the context of the present invention, it is the first operation of reading the outlines of the bezels of the rims of the frame that is of interest. Specifically, the optician needs to feel the inner outline of the rims of the selected eyeglass frame in order to determine accurately the coordinates of points characterizing the outline of the bottom of the bezel. Knowledge of this outline enables the optician to deduce the shape that is to be presented by each of the lenses once they have been shaped and beveled so as to enable them to be mounted in the frame.
In general, in order to perform this operation, the optician makes use of a bezel outline reader appliance of the kind described in document EP 0 819 967 or as described in document EP 1 037 008. Those appliances have a feeler suitable for pivoting about an axis of rotation that is normal to the mean plane of the frame and that comprises a feeler finger pointing along an axis orthogonal to said axis of rotation. The feeler finger includes in particular an end that is suitable for being inserted into the bezel in order to determine the three-dimensional coordinates of the outline of the bezel.
The particular purpose of this operation is to follow very exactly the bottom of the bezel included in each of the rims that is to be read so as to be capable of storing an accurate digital image of the shape of the bezel.
The Applicant has found that with certain shapes and sizes of frames, and in particular with frames that are strongly curved (i.e. present a large amount of curvature), known reading methods do not give complete satisfaction which can lead to difficulties in mounting lenses on frames of that type.